I'm learning about Turing reductions at the moment and I'm just wondering is there any difference between an oracle and a decider, As they seemingly do the exact same thing. I understand the point of a oracle is that we don't have to know how it gets its answer but it will always give us the right answer.
An oracle for a language B is an external device that is capable of reporting whether any string w is a member of B
which is the exact same thing as what a decider does. Is there any sort of difference between the two?